Optimum usage of automotive engines requires that engine run periods be long enough for the engine to become thoroughly heated. Short run periods can result in deposits which remain in the engine because they do not "burn off". An example of this phenomenon is spark plug fouling which occurs when an engine is started with a rich air/fuel mixture. A cold engine requires such a rich mixture for proper starting but a certain amount of the fuel remains in the liquid state and causes a deposit to form on the spark plugs. This is particularly true in the case of port injection engines which, due to the proximity of the injector to the cylinder, afford little time for injected fuel to vaporize. The deposit on the spark plug burns off if the engine runs long enough to get warm, but if the engine is subject to many consecutive short run periods the deposits will accumulate and become permanent; thus spark plug fouling results.
When a new vehicle is produced it is subject to a marshalling period before it is delivered to a customer. The marshalling comprises moving the vehicle short distances in the plant or to a holding area, loading onto a carrier for delivery to a dealer, and then further short moves while in the hands of the dealer. Each short move results in a short engine run period. The overall effect of the marshalling can be spark plug fouling.